This invention relates to high speed food processing machines in which a vertical drive shaft supports and drives food processing blades within an upwardly open food containing bowl. The bowl, which is closed by a lid during food processing, is pivoted for pouring its contents. Typically, a powerful motor on the bottom of the bowl rotates the drive shaft, and a mixing baffle blade is supported through the lid for rotation along and around the inside surface of the bowl for removing and returning foodstuffs from the side of the bowl to the vicinity of the food processing blades for further processing. The blades are removable and interchangeable, so that the blade or other tool configurations may be matched to the processing needs at hand. Machines of this type are highly effective in processing foods, and are so fast (many operations being performed in less than a minute), that the actual processing time is but a small part of the total "turn around" time. That is, it usually takes longer to load and unload the machine than to process the food once it is in the machine. It is therefore desirable to expedite the loading and removing operations as much as possible.
Due to the high speed of operation, it is also important to be able to observe the foodstuffs closely. When a processing operation extends over less than a few minutes, it is not practical to interrupt the operation every 10 or 15 seconds to check the condition of the food. There is thus a need for a practical, essentially continuous way to observe and monitor the progress of the food processing operation. Some prior art machines have perforated lids through which the foodstuffs may be observed, but this allows certain types of food to be thrown out through these openings. Transparent lids are unknown in commercial machines of this type, probably due to the structural problems of designing an effective transparent dome of the large size typical in such machines, and also because the view would be quickly obscured when foodstuffs were thrown against the lid by the high speed food processing blades.